Deflecting circuits



April 17, 1945. I -1' EATON 2,373,748

DEFLECTING CIRCUIT Filed Sept. 50, 1941 3 Sheets-Sheet 1 Snventor ThomdsZ Eatdn Gttmme gv April 1945- T. T. EATON DEFLECTING CIRCUIT Filed Sept.30, 1941 3 Sheets-Sheet 2 Zhwentor Thomas 1! Eaton attorney April 17,1945. T. T. EATON DEFLECTING CIRCUIT Filed Sept. 30, 1941 :s s am-shed sIII ZSnventgr Eaton (Ittomeg V min i T Thomas 11 the accompanyingdrawing'sin which eases e i7, recs nEFLEo'riNG omcurrs Thomas T. Eaton,Haddon Heights, N. J., assignor to Radio Corporation of America, acorporation of Delaware Application September, 3 941, Ser l No. 413,065(Claims. 01, 175 .335)

My invention relates to cathode. ray deflecting circuits andparticularly to deflecting circuits which produce sawtooth deflectingwaves.

An object of the invention .is to' provide an improved method of andmeans for causing a flow of deflecting current of thedesired wave formthrough deflecting coils having a substantial amount of distributedcapacity.

A further object of the invention is to provide an improved method ofand means for reducing or eliminating the efiects of distributedcapacity orthe like across deflecting coils.

A still further object of the invention i to pro- V magnetic verticaldeflecting circuits wave form distortiomand .capacity networks forcancelling capacity in horizontal deflecting circuits, 7

Figs. 4 to? show embodiments of the invention wherein negative feedbackis utilized in .electroto minimize Fig. 8 shows the use of negativefeedback in an electrostatic deflection circuit to minimize wave formdistortion. I

' In the several figures like parts'are indicated by the same referencecharacters.

Referring to Fig. 1, the circuit comprises a con- 1 denser III which ischarged slowly through a revide an improved method and means for mini- 4mizing any distortion of a sawtooth wave'introduced by amplifier tubesor other partsof a channel through which the sawtooth wave is passed.

y In one embodiment of the invention as applied to the horizontaldeflection circuit of a, television receiver, for example, thedistributed capacity of the deflecting coils is made inefiective in thecircuit by connecting a negative capacity circuit to the deflectingcoils. This negative capacity can be made to cancel out any undesiredcapacity l across the deflecting coils. In thi way -I avoid thenecessity of employing a damping tube or the like across the deflectingcoils to reduce the. transient otherwise caused at the end of eachdeflection by the distributed capacity.

Since my horizontal deflecting circuit contains no damping tube it isnow possible to utilize a negative feedback circuit to remove any waveform distortion that may be introduced in the circuit following thesawtooth generator or other point where the wave has the desired 'waveform. The voltage that is fed back preferably i taken from across aresistor connected in series with the deflecting coils. v

In otherembodiments of the invention, the negative capacity network isemployed to improve the deflection circuit operation without em.-ploying a negative feedback circuit in combination with it.

In still other embodiments of the invention, especially as applied tovertical deflecting circuits, negative feedback circuits are employedwithout the use of negative capacity circuits.

The invention will be better understood from the following descriptiontaken in connection with Fig. 1 is a circuit diagramof-an embodiment ofmy invention as applied to the horizontal deflecting circuit of atelevision receiver,

Figs. 2 and 3 are circuit diagrams'showing'other embodiments of theinvention utilizing negative sistor ll andthen discharged rapidlythrough a discharge tube 12 in response to the application of a pulse onthe grid of the tube whereby a sawtooth voltage wave appears across thecondenser.

deflecting coil .The sawtooth voltage wave is amplified by resistancecoupled amplifiers l4 and i6 and applied to the control grid of apentodeH which func-' tions as the output tube supplying sawtooth current to apair of deflecting coils I 8.

Amplifier tubes l4 and i6 maybe suitably biased by means of cathoderesistors 2| and 22, respectively, to function as' linear amplifiers.

Output tube i1 is also biased tofunction as a,

class A amplifier, the bias being providedby a cathode resistor 23c23b'which is common to the tube l1 and 'to a vacuum tube 24 described below.F r

The deflecting coils 18 have condenser 26in series therewith to blockthe "D.-C. component,

the plate voltage for tube I! being applied through a choke coil 21. a

A resistor 28 is also connected in series with the deflectingcoils inorder to obtain a feedback voltage having the same wave shape as thedeflecting current as Will be described hereinafter.

The circuit so far described may not be verysatisfactory if thedeflection is to occur at a comparatively high frequency such as 13,290per second commonly employed for the horizontal deflection in atelevision system. The main reason across the deflecting coils l8 whichis indicated at 30. This V is mainly the distributed capacity of thecoils, but it also includes any other capacity across the coils such astube capacity.

A well known way of reducing or eliminatingtransients caused by thecapacity 30 i to connect a damping tube across the deflecting coils. If

this is done, however, the feedback correction circuit describedhereinafter cannot be employed I since a substantial amountof the outputtube current goes into the damping circuit.

The negative capacity network, which will now be described, makespossible the use of the feedback correction in a horizontal deflectingcircuit or the like having a large amount of distributed capacity.

The negative capacity network comprises the vacuum tube 24, which isshown by way of example as a pentode, having its control grid 3|connected to a phase shifting circuit consisting of a condenser 32 and alow resistance resistor 33 connected in series with each other betweenthe plate of output tube i1 and ground. A suitable negative bias ismaintained on the grid 3| by a grid leak connection 36 to a point on thecathode resistor 23a23b whereby the tube 24 operates over asubstantially linear part of its characteristic. The usual positiveoperating voltages are applied to the plate and screen grid of tube 24.

The basic operation of the negative capacity network is similar to thatof the well known reactance tube circuits employed for automaticfrequency control and for frequency modulation Specifically, plate,current from the tube Il' passes through the phase shifting circuit 32-33 whereby a voltage appears across the resistor 33 which leads thevoltage at the plate of tube H by substantially 90. It is this leadingvoltage that is applied to the grid 3|. The plate current of the tube 24will be in phase with the said voltage on its grid whereby this platecurrent and the corresponding voltage drop in cathode resistor 25a-23balso lead by substantially 90 the voltage at the plate oftube I'l.

Since the voltage drop in cathode resistor 23a- 23b is applied to thecathode of tube 11, the current component produced by it in the platecircuit is reversed in phase. 'I'hus, the 90 leading voltage at thecathode of tube l'l produces a 90 lagging plate current component, itbeing assumed that the plate circuit-is resistive. This is a properassumption since the plate-cathode impedance of a pentode is very highcompared with the impedance of the deflecting coils.

From the foregoingit will be apparent that by properly adjusting the tapon the phase shift resistor 33, the magnitude of the above-described 90?lagging current component can be made equal to the 90 leading currentcomponent caused. by the distributed capacity 30. In other words, I haveintroduced a negative capacity that balances out the capacity 30.

A negative feedback circuit may now be utilized to make the deflectingcurrent in coils l8 have the same wave shape as the wave shape ofthevoltage appearing on the plate of amplifier tube I4. It will beunderstood that while a voltage having a good sawtooth shape may beproduced without much difiiculty, it generally has been diflicultto makethe final deflecting cur-' I rent have exactly the same shape. Forexample, the characteristics of the amplifier tubes l6 and I! may departenough from linearity to introduce distortion. p

In the example shown in Fig. 1, the voltage across the low impedanceresistor 28 is fed back to an amplifier tube 4! which is biased by acathode resistor 42 to function as a' linear amplifier. The tube-4i andthe tube 14 have a common plate resistor 43 whereby their outputs addalgebraically. Since these outputs are 180 out of phase any departurefrom the desired wave bring the deflecting current wave shape very closeto the wave shape of the input voltage, the exactness of the correctiondepending upon the gain in the feedback loop.

Fig. 2 shows another circuit that may be utilized for obtaining thedesired negative capacity.

A 90 shifting network 32-43 is connected from the plate of the outputtube H to ground as in Fig. 1. The leading voltage appearing acrossresistor 33 is amplified by an amplifier tube 46 and applied to thecontrol grid of a pentode 41. The plate of pentode 41 is connected tothe plate of the output tube ll whereby a 90 lagging current is suppliedto balance out the 90 leading current taken by the distributed capacity30. The cathode resistors 48 and 49 are provided to bias the tubes 46and 41, respectively.

Fig. 3 shows another example ,of negative ca pacity circuits that may beemployed in practicing the invention. Here the leading voltage acrossresistor 33 "is applied to an amplifier tube 5|. The plate resistor 52is common to the amplifiers 5| and I6 whereby the reactive voltagecomponent is added to the sawtooth voltage supplied through the tube It.Thus the desired 90 lagging current component appears-in the platecircuit of the tube l1.

Fig. 4 shows a negative feedback circuit for reducing sawtooth wavedistortion in a vertical deflecting circuit which does not require anyspecial circuit for eliminating distributed capac- Since the variouselements for this circuit are substantially the same as in thehorizontal deflecting circuit except for the circuit constants,corresponding parts are indicated by the same reference numerals.

The deflecting coil current passes through the coils 18 in parallel,through a resistor 54 which may be provided to help in obtaining astraight sawtooth shape, and through the blocking condenser 26 and theresistor 28. The lower end of resistor 54 may be connected to a voltagedivider shape of the deflecting current will cause a cor- 56 through avariable tap for centering purposes.

As-in the circuit of Fig. 1, the voltage drop across resistor 28 is fedback to an amplifier tube 4| which introduces negative feedback at theinput circuit of amplifier It to remove distortion introduced byamplifiers l6 and I1, and by distributed capacity, etc., in the outputcircuit of the tube l1.

condenser I0 is connected through resistor 28 to ground whereby thevoltage across resistor 28 is added algebraically to the desiredstraight sawtooth produced across condenser M.

.Fig. 6 shows a, vertical deflecting circuit similar to that of Fig. 5in that the negative feedback resistor 28 is included in the sawtoothgenerator itself. The said generator comprises a vacuum tube 6| having acondenser '62 connected between the cathode of tube GI and ground and inseries with resistor 28. The condenser 52 is charged through the tube 6|upon reception of a positive pulse and is discharged comparativelyslowly through the shunting resistor 83. Since the resulting sawtoothvoltage across condenser 82 is of reversed polarity as compared withthat produced amplifier stage may be omitted and the feedback voltagewill be the correct polarity.

Fig. 7 shows a circuit in which the feedback voltage is fed into thecathode circuit of asvavss circuit is taken 05 a resistor H' in thecathode Also, an additional amplifier stage 72 is employed to obtain thecorrect feedcircuit of tube ll.

back. polarity. Itwill be noted that sawtooth voltages of oppositepolarity are obtained from i the plate and cathode circuits of tube i ito apply the deflecting voltages in balanced relation to th deflectingplates (not shown) It will be appareat that any departure from thedesired voltage wave form in the said plate and cathode circuits will becorrected by the negative feedback.

I claim as my invention 1. A horizontal deflecting. circuit comprising apair ofdeflecting coils having undesired dis-.

' tribute-d capacity thereacross, means for produc- 4 m a' voltagehaving a certain wave form, an amplifier tube having a platecircuitcoupled to said coils and having an input circuit coupled to saidvoltage producing means, means comprisinga negative capacity network ofthe reactance' tube type for cancelling out at least a substantial partof said distributed capacity, means for obtaining a voltage having thesame wave shape as that of the current flowing through said coils, and a-'negativefeedback circuit for feeding back said second vole to a pointwhere said flrst voltage appears for reducing distortionin the waveshapeof said current. i a

, 2.1m electromagnetic deflecting circuit com-. pg apair of deflectingcoils having'undesired distributed capacity thereacross, a vacuum tubeconnected to supply plate current to said coils, a phase shiftingnetwork connected across said coils to produce avoltage having areactive component, an amplifier tube having an input circuit to whichsaid voltage is applied and means'for so connecting the output circuitof said amplifier tube to said deflecting circuit that there is producedin said coils a lag ing current component to cancel the leading currentcomponent caused by said distributed capacity.

3. An electromagnetic deflecting circuit comprising a pair of deflectingcoils having undesired distributed capacity thereacross, means for'obetaining a voltage having a reactive component 90 degrees out of phasewith respect to the volt- I age across said coils, and means includingan amplifier upon whichsaid reactive component is impressed forsupplying to said coils a lagging currentto' cancel at least part 01 theleading current caused by said distributed capacity.

4. An electroetic deflecting circuit comprising a pair of deflectingcoils having undesired 7 capacity thereacross, a vacuum tube connectedto supply plate current to said coils, a phase shifting networkconnected across said coils to produce a voltage having a reactivecomponent, an amplifier tube having an input circuit to which saidvoltage is applied, means for so connecting the output circuit of said.amplifier tube to said deflecting circuit that there is produced in saidcoils a lagging current component to cancel the leading was currentcomponent caused by said distributed capacity, means comprising a lowresistance resister in series with s'aid'deflecting coils for obvtaining a voltage having the same wave shape as that of the currentflowing through said coils, and means comprising a negative feedbackcircuit for feeding back said voltage to reduce distortion in the waveshape-oi said deflecting coil current.

THOMAS T. EATON.

